The current development state of information technology emphasizes the use of display devices as a preferred medium for communicating information to user. Examples of display devices include flat panel displays, such as organic light emitting diode (OLED) displays and liquid crystal displays.
In general, display devices, such as flat panel displays, include a display panel including a plurality of pixels arranged in a matrix or array form and a driver for driving the pixels and other components of the display panel. In the case of color display panels, each pixel may be divided into red, green, and blue subpixels for the reproducing a range of colors. The driver may include a scan driver for supplying a scan pulse to the display panel and a data driver for supplying a data signal to the display panel.
The scan driver typically supplies the scan pulse to scan lines to progressively select each row of the subpixels of the display panel to operate, and the data driver typically supplies the data signal to data lines associated with each of the different columns of subpixels in the display panel. In operation, data signal is supplied for subpixels in the row selected by the scan pulse, and the selected subpixels emit light in response to the data signal. This process is repeated for all rows to cause the display panel to display an image.
In some configurations, the scan driver may shift the scan pulse from scan line to scan line using a shift register. For this purposes, a shift register may have a plurality of stages connected to the scan lines, where each stage is comprised of a plurality of transistors. Preferably, a stage has to stably maintain a voltage of the scan line connected to the stage. However, in some instances some of nodes inside the stage may be unbiased, and thus floating, during the operation of the scan driver. Due to this, these floating nodes are easily affected by external noise because no voltage supplied to these floating nodes. Unfortunately, these floating nodes may be affected by an external noise and thus may lead to several abnormal operations including changes in the voltage of the scan line, etc., which can cause abnormal operation for he the display panel.
Moreover, the lifespan of the transistors in the stages may be reduced because of a stress due to any charge remaining in the floating nodes. In certain configurations, such charges can persist for a significant period of time. In particular, because an off-current of a transistor using an oxide semiconductor is very low, it can take a relatively long time to naturally discharge any remaining charge at the gate of the transistor. Therefore, the transistor is stressed by these remaining charges.